Recently, non-orthogonal multiple access (NOMA) has been recognized as a potentional technology for the next generation mobile communication networks to tackle the explosive growth of data traffic [1]}, [2]}, [3]}, [4]}, [5]}.
Due to superposition coding at the transmitter and successive interference cancelation (SIC) at the receiver, NOMA can achieve higher spectral efficiency than conventional orthogonal multiple access (OMA), such as time division multiple access (TDMA) and orthogonal frequency division multiple access (OFDMA).
Many previous contributions [6]}, [7]}, [8]}, [9]}, [10]}, [11]}, [12]}, [13]}, [14]}, [15]} only considered OMA.
Motivated by the benefits of NOMA over OMA, a NOMA-based MEC network was investigated in [16]}, where users simultaneously offload their computation tasks to the BS and the BS uses SIC for information decoding.
Besides, both NOMA uplink and downlink transmissions were applied to MEC [17]}, where analytical results were developed to show that the latency and energy consumption can be reduced by applying NOMA-based MEC offloading.
Time and energy minimization were respectively optimized in [18]} and [19]} for NOMA-based MEC networks with different computation deadline requirements for different users.
However, [16]}, [17]}, [18]}, [19]} only considered one group of users forming NOMA and ignored the time allocation among different groups of users forming NOMA.
Since each resource is recommended to be multiplexed by small number of users (for example, two users) due to decoding complexity and error propagation [24]}, it is of importance to investigate the resource allocation among different groups of users forming NOMA.
